This invention relates to a dilator for use in opening the lumen in tubular body organs such as in percutaneous transluminal coronary angioplasty (PTCA) and in particular to a dilator utilizing a material having a negative Poisson ratio which expands in thickness upon stretching to thereby open the lumen.
PTCA is the most frequently performed coronary revascularization procedure. Most PTCAs are balloon angioplasties, a procedure in which a balloon is inserted through the patient's vascular system to the site of an atheroma and inflated to compress, reshape and redistribute the accumulated material comprising the atheroma. A marked increase of blood flow through the artery is provided in most cases.
While balloon dilation catheters have been extremely successful in performing angioplasty, there are several disadvantages to a balloon catheter. The primary disadvantage or problem with the balloon catheter is its size. Use of balloon catheters is currently restricted to the larger coronary arteries. A device which can be used to perform PTCA in small coronary arteries would have a tremendous benefit in terms of improving the supply of blood to the heart. Other disadvantages of balloon catheters include problems with control of the inflation pressure, maintenance of the balloon position while the pressure is applied and complications arising from bursting of the balloon. The extent of balloon expansion as it is inflated is difficult to control and varies depending upon the resistance provided by the artery itself. It is easy to over inflate the balloon, applying excessive pressure directly on the atheromatous lesion and damaging the wall structure of the artery.
Accordingly, it is the object of the present invention to provide a dilator which overcomes the above disadvantages and problems associated with balloon dilation catheters.
It is a further object to provide a dilator in which the radial expansion of the dilator is both known and controllable.
The dilator of the present invention utilizes a hollow rod of expanded polytetrafluorethylene (PTFE) having a negative Poisson ratio. The Poisson ratio of a material relates stretching to thinning. Most materials tend to roughly maintain their volume when stretched or compressed. As a result, when stretched, most materials will thin and when compressed they become thicker. However, it has recently been discovered that expanded PTFE behaves in the opposite manner, i.e. it becomes thicker when stretched rather than thinner. Such a material is said to have a negative Poisson ratio.
The dilator includes a hollow rod or sheath of the PTFE near its distal end. When placed in the coronary artery at the desired location, it is pulled lengthwise, stretched, so as to expand radially outwardly, applying pressure to the atheroma in the artery and, as a result, compresses, reshapes and redistributes the accumulated material opening the lumen of the artery.
The use of a negative Poisson ratio material in a dilator avoids the need to inflate an expandable member such as a balloon to compress the atheroma. Without the need for inflation, there is no concern with control of inflation pressure or problems associated with a leak of the inflation medium. The amount of radial expansion of the PTFE can be easily controlled by the physician performing the procedure by controlling proximally the amount of stretching of the PTFE. Dilators can be made with various diameters to suit the needs of individual patients.
During an angioplasty procedure, several dilators can be used in a series with each successive dilater having a slightly larger diameter and slightly larger controlled distention.
While the invention is described in the context of a dilator for use in coronary angioplasty, it should be understood that the dilator can be used in any procedure which opens the lumen of a body structure by the application of pressure from within the lumen, e.g. including opening of occluded fallopian tubes or cystoscopic relief of closing of the urethra associated with prostatitis.
Further objects, features and advantages of the invention will become apparent from a consideration of the following description and the appended claims when taken in consideration with the accompanying drawings .